Electronic interval timer



Jan. 16, 1951 G. D. HANCHETT, JR 2,538,515

ELECTRONIC INTERVAL TIMER Fil ed June 25, 1947 INVENTOR. 60GED him cw, J2.

Aff om e7? comprising two resistors, Hand" 52'.

Patented Jan. 16, 1951 UNITED s ms PAT NT 2,538,515 ELEcTno io'iN'rERvAL TIMER George D; Hanch'ettJJL, MilburmN. 3., assignor to Radio.- Corporation of America, a

ofv Delaware corporation 2 dams. (-01. 250-41) "My invention relates to a controlcircuit-and more particularly to a control circuit in which. thecontrolis provided by the periodic conduction ofa pair of gas dischargetubes.

For many uses, ithas been found desirable to provide apparatus for controlling any suitable load device which will be alternately energized andde-energized at definite,predetermined in tervals. Many such devices have heretoforebeen proposed, but not any of them, insofar as I am aware, hasbeen-entirelysatisfactory'because: they were more or less uncertain in their operation and complicatedinconstructioni It is an object of my invention to provide a. simple control circuit in which both thejperiodic- 1 ity of energization of the load device and. the

duration of the period of energization of such.

device may beaccurately predetermined.

A further objectiof' my invention is the provision of a circuit arrangement whereby; selection is provided for the duration of the period of "one" ergization of the. load. device for each chose-n frequency of cyclic-operation. l In. general; I have provided a pair. of-gas disohargetubes connected in an; oscillatory circuit, said circuit utilizing. grid potential. storage means wherein the timeconstants of the-said grid po-= t'ential storage means may be independently var ied. Selectivemeans is provided. in the" anodeoutput circuits of the gas-dischargetubesifor.the

purpose of'permittingthe energization of a load device by the output of either of the tubes.

A better understandingofmy-invention may be had frornithe"followingxdescription ofaparticular embodiment of my invention taken in conjunction with the. accompanying drawing'in which the single figure represents schematically one portion of. whicliisutilized for grid bias on the gas discharge tubes. This biasing potential is controlled and regulatedbymeans. of a voltage regulator, III and apotential d'ivider,.tlie latter obvious that the ratio of the values of the resistors forming the potential divider may be chosen to bias the gas discharge tubes to any desired level. The anode 5 of the gas discharge tube I is connected to one side of a reversing switch 2| and also to a capacitor 19. In the It Will be.

I z charging circuit of capacitor [9, thereis provided a fixed resistor l1 and a variable'resistonflfl" Similarly, the anode 6 of the gasdischa-rge tube 2 is connected to the other side ofthe reversing switch and to a capacitor 201 In thcharg g circuit of this capacitor, there is likewise p vided a fixed resistor l4; and a variable resistor [3. The gas discharge tubes are provided-lwith grid resistors, l5 and I8, respectively, thegrid sistor of the gas discharge tube I bcing'connecteii to the charging circuit of the capacitor 28 be: tween it and the fixed resistor I4", the'grid re sistor E8 of the gas discharge tub'e 2' being "can nected' between the capacitor [9 and the fiiied 'resistor l1, 1 5

One of the center" taps of the reversing" switch 21' is connected through the coil of a relay 22th the supply line; while the other centertap ofsucfi switch is connected through a resistor 23' tothe supply line; Between the two center taps crthe reversing switch there connected 2.- capacitdr" s I To initiate the operation of thesysteni, there-3 versing switch is put in an openpositioil-and electrical energy is applied taper-mt the elements flow will be completed through the resistor the capacitor [9, and the resistors if and l61 A path will also be completed through the coil-of the? relay 22,.the capacitor 26, and the resistors l3- and'il As a result, the capacitors I a and 0 start to charge; However, since-thetimeconst t: ofthe circuit through capacitor i9 is less than'ithetime constant of the circuit through capacitor? 20, theanode' 5 of the gas discharge tube I will,

reach firing potential before the anode 6 of the; gas discharge tube 21 When the gas discharge" tube I conducts, current flows through resistor23,

and the potential diiierence' across the tube [is greatly reduced causing, in efiect, a negativepulse; to be transmitted across capacitors Hand 24. The pulse across thecapacitor 24' willbe reflected at the anode 5 of the gas discharge tube 2pre1-. venting its firing; This pulse is quickly dissi pated, however, sin'cethe time con'stant-of the At thecircuit including capaei'tbr 2i! short. same time the pulse across capacitor I9 is reflected on the control grid 8 of the gas discharge tube 2, further preventing the firing of such tube. ,:,,S. .nce the time constant of the circuit including For e'Xainple' it is assumedthat capacitor I9 is longer than that including capacitor 24, the effect of the negative pulse will exist on the control grid 8 of the gas discharge tube 2 much longer than on its anode. Therefore, although the anode 6 may reach firin potential, the control grid 8 will'prevent conduction until the capacitor I9 has discharged, and when such capacitor discharges sufliciently the gas discharge tube 2 will fire, causing current to flow through the coil of relay 22, thus closing it and keeping i it closed for as long as such tube 2 is conducting.

This flow of current greatly reduces the potential drop across the gas discharge tube 2 which, in effect, causes a negative pulse to be transmitted across the capacitors 20 and 24. The negative pulse across capacitor 24 is reflected at the anode of the gas discharge tube I causing it to be extinguished. At the Same time the negative pulse across capacitor 2|] is reflected at the control grid I preventing the 'refiring of the gas discharge tube I. The pulseacross capacitor 24 is quickly dissipated and the anode 5 of the gas discharge tube I is restored to firing potential. However, because of the length of the time constant oithecircuit including capacitor 20, the control grid 1 will prevent the firing of tube I 'until capacitor has sufficiently discharged.- When the gas discharge, tube I fires, the operation is reversed, extinguishing the gas discharge tube 2 which allows the relay to return to its former position. The action described above is then repeated causing the continuous on and off operation of the relay.

Itmay be seen from the foregoing description that, because of th difierence in the time con stantsof the circuits, the gas discharge tube I will conduct for a shorter time each cycle than the gas discharge tube 2. If the switch 2I had been closed to the side marked Short, the only difference in the circuit would have been that the relay 22 would have been in the anode circuit of the gas discharge tube I and the resistance 23 would'have been inthe anode circuit-of the gas discharge'tube 2. V This would mean that the relay would have'been closed for a shorter. tim each cycle. 1 7

Further, it may be seen that by varying either or both'of theresistors I3 and I6, any desired periodicity of operation, and any relay closed-time duration may be obtained, within the limits of the particular elements of the circuit.

, The positive grid bias is utilized and so chosen to cause the firing of the gas discharge tubes I and 2 before the grid charging curve deviates from its linear slope.

While I have described my invention in a particular arrangement for the purpose of illustration, it will be understood that the general principlesof my invention may be applied to other and widely varied organizations without departing from the spirit of my invention and the scope of the appended claims.

WhatI claim is: I f 1. In a control circuit, a source of direct current potential, a first gas discharge tube, having a cathode, an anode and a control grid, a second gas discharge tube having a cathode, an anode and a control grid, a point of fixed reference p0 tential, said'cathodes being connected to said point, a source of positive biasing potential connected to both of said control grids, a first ca- 4 c pacitor-resistor network constituting a potential storage means connecting the output of said first tube to the control grid of said second tube, the potential stored insaid first network being applied between the cathode and control grid of said second tube, a second capacitor-resistor network constituting a second potential storage means connecting the output of said second tube to the control grid of said first tube, the potential stored in said second capacitor-resistor network being applied between the cathode and control grid of said first tube, a capacitance connecting the outputs of both of said tubes, a load device, an impedance, a switching device connecting said load device in series with the space discharge path of either of said tubes and said source of direct current potential and simultaneously connecting said impedance in series with the space discharge path of the other of said tubes and said source of direct current potential.

' 2. In a control'circuit, a source of direct current potential, a first gas discharge tube, having a cathode,- an anode and a control grid, a'second gas discharge tube having a cathode, an anode and a control grid, a point of fixed referenc potential, saidcathodes being connected to said point, means providing'a source of positive biasing potential connected to both of said grids, a first capacitor-resistor network connecting the output of said first gas discharge tube to the control grid of said second-gas discharge tube, the potential stored in said first capacitor-resistor network being applied between the cathode, and controlgrid of said second gas discharge tube, a second capacitor-resistor network connecting the output of said second gas discharge tube to the control grid of said first gas discharge tube, the

' potential stored in said second capacitor-resistor network being applied between'the cathode and control grid of said first gas discharge tube, the

time constants'of said capacitor-resistor networks;

being independently variable, aload device; animpedance, a switching device connecting said load device in series with the space discharge path of either of said gas discharge tubes'and said source of direct current potential, said switching device simultaneously connecting said impedance in series with the space discharge path of the other of said gas discharge tubes and said source of direct current potential;

GEORGE D. HANCHETT, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED'STATES PATENTS I Name Date Stansbury Sept, 12,1933 Stansbury Apr. 10, Stansbury Apr. 10, Stansbury Dec. 3l,

OTHER REFERENCES Number 

